1. Field of the Invention
This invention relates to a spread illuminating apparatus for a display portion of a personal computer or the like, in particular, for using as an illuminating means of a portable type of liquid crystal display apparatus.
2. Conventional Art
For a display of a personal computer, a cathode ray lamp (so called a picture lamp) has been used primarily. However, since it is large in size, heavy in weight and high in electric power consumption, recently a liquid crystal panel has been heavily used. Further, such panels have been used also for information terminal appliances such as a note book type of personal computer or portable telephone.
As mentioned above a demand for a liquid crystal panel has been rapidly increased, but since the liquid crystal panel itself does not emit light, an illuminating apparatus becomes necessary. Particularly, in recent demand for a lower profile, an illuminating apparatus of thin plate-like side light system has been used as an illuminating means.
Conventionally, a cold cathode fluorescent lamp or a hot cathode fluorescent lamp has been used as this illuminating apparatus. In either case, a fluorescent lamp needs a high voltage for discharging between electrodes and electric energy consumption has to be large. In particular for a portable type, the electric power generated from a battery is consumed mostly by this illuminating apparatus.
Therefore, an illuminating apparatus which uses a white emitting diode in place of fluorescent lamp has been developed and the patent application has been filed (see Patent application No. Hei 10-182076) by the inventors of the present invention. This system is explained based on FIG. 3 as an embodiment which is used for a reflection type of liquid crystal panel. A transparent substrate 1 is thin plate-like, along one side of which a bar-like light conductive member 2 is disposed. On one portion of the light conductive member 2, an optical path conversion means is provided as later described.
On at least one end of the light conductive member 2, a light emitting diode 3 (LED) as an emitting body is disposed. This light emitting diode 3 has a white luminescent color, and is adapted to be surrounded with a case having a light reflection function in such a manner as, when it is supplied with electric current and emits light, most of rays of light enter the light conductive member 2. Under this structure, when the light emitting diode 3 emits light, the ray of light proceeds toward the transparent substrate 1 through the light conductive member 2 and the emitted light illuminates a liquid crystal panel 4.
Thus, the light conductive member 2 has a function to convert the direction of the rays of light coming from the light emitting diode 3 at 90 degrees toward the transparent substrate 1, and in order to carry out its conversion well, a light reflection pattern with a plurality of grooves 2a shaped triangular in section and separated at a regular spacing with each other is formed on one of the surfaces. Now, a plane portion 2b is formed between the grooves 2a. 
Under this structure, the light emitted from the LED 3 enters the inside of the light conductive member 2 at one end thereof, strikes the groove 2a as a light reflection pattern and proceeds from the light conductive member 2 toward the transparent substrate 1.
Further, between the transparent substrate 1 and the light conductive member 2, a light diffusion plate 5 is provided. when the rays of light emitted from LED 3 enters the light conductive member 2, only the groove 2a is brightened, rendering the groove 2a bright and the plane portion 2b dark, so that, when viewing the transparent substrate 1, a stripe pattern: of light and shade is seen. The diffusion plate 5 is provided to solve the above mentioned problem in such a manner as the rays of light are intermixed for a uniform brightness while travelling through the diffusion plate 5.
By the way, an emitting distribution of the emitted light of the spot-like light source like a light emitting diode has a characteristic with a specific emitting distribution as shown in FIG. 4 in which axis of ordinates represents a relative brightness indicating the intensity level. The emitting distribution from the light conductive member 2 when the light enters the light conductive member 2 as shown in FIG. 5, toward vertical direction, has a characteristic as shown in FIG. 6 which is not different from the one shown in FIG. 4 where the light does not go through the light conductive member 2. Toward the horizontal direction, the emitting distribution becomes as shown in FIG. 6 due to the groove 2a as a light reflection pattern shown in FIG. 5.
Further, by disposing the light diffusion plate 5 as shown in FIG. 7, the light emitting distribution spreads toward both vertical and horizontal directions as shown in FIG. 8. If it is disposed close to the transparent substrate 1 as shown in FIG. 9, the light emitting distribution toward the vertical direction is controlled as shown in FIG. 10 due to the light reflection pattern la formed on the transparent substrate 1, but no change is seen toward the horizontal direction.
Now, the above spread illuminating apparatus as an illuminating means for a liquid crystal display apparatus contains the following problem. That is, the light of large angle portion shown in FIG. 10 is located out of the field of view and is not usable. The present invention was made in the light of this point in a spread illuminating apparatus in which a bar-like light source is disposed close to the side of a transparent substrate made of a transparent material. The purpose is to make usable the unusable light located out of the field of view, in other words, to turn rays of light into the field of view in order to attain a brighter illumination.
According to a first aspect of the present invention, in a spread illuminating apparatus in which a bar-like light source formed with a light conductive member made of a transparent material and a spot-like light source provided at at least one end of the light conductive member is disposed close to a transparent substrate made of a transparent material, the light conductive member is provided with an optical path conversion means and an optical path conversion plate is disposed between the transparent substrate and the light conductive member.
According to a second aspect of the present invention, in a spread illuminating apparatus in the first aspect, the optical path conversion plate is provided with a row of prisms as an optical conversion means disposed on the other side of the optical path conversion plate than a side facing the transparent substrate.
According to a third aspect of the present invention, in a spread illuminating apparatus in the first or second aspect, a reflection plate of a white or metal vaporized film or the like is provided on the side of the light conductive member opposite to a side facing the optical path conversion means.
According to a fourth aspect of the present invention, in an illuminating apparatus in any one of the first to third aspects, the optical path conversion means of the light conductive member is formed with prism grooves in such a manner as hypotenuses of triangle are continuously disposed on one surface of the light conductive member.
According to a fifth aspect of the present invention, in a spread illuminating apparatus in any one of the first to third aspects, the optical path conversion means of the light conductive member is formed with the means of light dispersion consisting of minutely rugged surfaces.
According to a sixth aspect of the present invention, in a spread illuminating apparatus in any one of the first to third aspects, the optical path conversion means of the light conductive member is formed by applying an opaline coating containing light dispersive substances to one surface of the light conductive member.
By such constitution, the light which is emitted from the spot-like light source and enters the light conductive member exits slantingly due to the optical path conversion means.
This light, after entering the optical path conversion plate slantingly, enters the transparent substrate straightly due to the optical path conversion plate to improve the efficiency of the emitting distribution from the transparent substrate for illuminating the liquid crystal panel with a high brightness.